Alternative mechanisms for O2release and O–O bond formation in the oxygen evolving complex of photosystem II

2015 ◽  
Vol 17 (18) ◽  
pp. 12168-12174 ◽  
Author(s):  
Xichen Li ◽  
Per E. M. Siegbahn
Keyword(s):  
Photosystem Ii ◽  
Transition State ◽  
Bond Formation ◽  
Oxygen Evolving Complex ◽  
Competitive Mechanism ◽  
The One ◽  
Oxygen Evolving

A new transition state for O2release has been found. An alternative, nearly competitive, mechanism for O–O bond formation is described, which is very similar to the one previously suggested.

Electronic structure of the oxygen-evolving complex in photosystem II prior to O-O bond formation

Science ◽  
2014 ◽  
Vol 345 (6198) ◽  
pp. 804-808 ◽  
Author(s):  
N. Cox ◽  
M. Retegan ◽  
F. Neese ◽  
D. A. Pantazis ◽  
A. Boussac ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Photosystem Ii ◽  
Bond Formation ◽  
Oxygen Evolving Complex ◽  
Oxygen Evolving

Large-scale QM/MM calculations of the CaMn4O5 cluster in the S3 state of the oxygen evolving complex of photosystem II. Comparison between water-inserted and no water-inserted structures

2017 ◽  
Vol 198 ◽  
pp. 83-106 ◽  
Author(s):  
Mitsuo Shoji ◽  
Hiroshi Isobe ◽  
Takahito Nakajima ◽  
Yasuteru Shigeta ◽  
Michihiro Suga ◽  
...  
Keyword(s):  
Photosystem Ii ◽  
Water Oxidation ◽  
Large Scale ◽  
Geometrical Structure ◽  
Bond Formation ◽  
Oxygen Evolving Complex ◽  
Computational Results ◽  
Hydroxide Anion ◽  
The Right ◽  
Oxygen Evolving

Large-scale QM/MM calculations were performed to elucidate an optimized geometrical structure of a CaMn4O5 cluster with and without water insertion in the S3 state of the oxygen evolving complex (OEC) of photosystem II (PSII). The left (L)-opened structure was found to be stable under the assumption of no hydroxide anion insertion in the S3 state, whereas the right (R)-opened structure became more stable if one water molecule is inserted to the Mn4Ca cluster. The optimized Mna(4)–Mnd(1) distance determined by QM/MM was about 5.0 Å for the S3 structure without an inserted hydroxide anion, but this is elongated by 0.2–0.3 Å after insertion. These computational results are discussed in relation to the possible mechanisms of O–O bond formation in water oxidation by the OEC of PSII.

scholarly journals Mechanism and energy diagram for O–O bond formation in the oxygen-evolving complex in photosystem II

2007 ◽  
Vol 363 (1494) ◽  
pp. 1221-1228 ◽  
Author(s):  
Per E.M Siegbahn
Keyword(s):  
Photosystem Ii ◽  
Bond Formation ◽  
Oxygen Radical ◽  
Oxygen Evolving Complex ◽  
Spin Alignment ◽  
Energy Diagram ◽  
Oxo Ligand ◽  
Oxygen Evolving ◽  
Rate Limiting ◽  
Good Agreement

The recent finding of a transition state with a significantly lower barrier than previously found, has made the mechanism for O–O bond formation in photosystem II much clearer. The full mechanism can be described in the following way. Electrons and protons are ejected from the oxygen-evolving complex (OEC) in an alternating fashion, avoiding unnecessary build-up of charge. The S 0 –S 1 and S 1 –S 2 transitions are quite exergonic, while the S 2 –S 3 transition is only weakly exergonic. The strong endergonic S 3 –S 4 transition is a key step in the mechanism in which an oxygen radical is produced, held by the dangling manganese outside the Mn 3 Ca cube. The O–O bond formation in the S 4 -state occurs by an attack of the oxygen radical on a bridging oxo ligand in the cube. The mechanism explains the presence of both a cube with bridging oxo ligands and a dangling manganese. Optimal orbital overlap puts further constraints on the structure of the OEC. An alternating spin alignment is necessary for a low barrier. The computed rate-limiting barrier of 14.7 kcal mol −1 is in good agreement with experiments.

scholarly journals O-O Bond Formation in Photosystem II Oxygen Evolving Complex

2018 ◽  
Vol 114 (3) ◽  
pp. 520a ◽  
Author(s):  
Yulia Pushkar ◽  
Scott Jensen ◽  
Katherine Davis
Keyword(s):  
Photosystem Ii ◽  
Bond Formation ◽  
Oxygen Evolving Complex ◽  
Oxygen Evolving
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